Particle Effects on Heart-Rate Regulation in Senescent Mice

Abstract

Because epidemiology studies consistently identify the elderly at risk for air pollution-related morbidity and mortality, we developed a model of senescent-dependent susceptibility based on indices of physiological aging. In the current study, we hypothesized that heart-rate regulation during particulate matter (PM) exposure differs with senescence-dependent susceptibility owing to variation in autonomic nervous control. Heart rate (HR) and heart-rate variability (HRV) parameters were measured from 162 samples of 2-min electrocardiograph (ECG) recordings in age-matched healthy (n = 5) and terminally senescent (n = 3) AKR mice during 3-h exposures to filtered-air (FA, day 1) and carbon black (CB, day 4; <200 µg/m 3 ). On day 1, HR was significantly (p < .01) depressed during FA in terminally senescent mice. By day 4, HR was further slowed significantly (p < .01) due to the effects of CB exposure for 3 days. The combined effects of terminal senescence and CB exposure acted to depress HR to an average (±SEM) 445 ± 40 bpm, or ∼80 bpm lower compared to healthy HR responses. The change in rMSSD, an HRV parameter corresponding to relative influences of parasympathetic tone on HR, was significantly (p < .01) greater on day 1 and day 4 in terminally senescent mice compared to healthy mice. In contrast, the LF/HF ratio, an HRV parameter derived from spectral analysis indicating relative changes in cardiac sympathetic tone, was significantly (p < .01) depressed in terminally senescent mice on day 1. By day 4, significant increases in LF/HF were evident in healthy mice during CB exposure, suggesting that HR regulation was associated with an increase in sympathetic tone. Alternatively, terminally senescent mice appeared to modulate a lower HR without change in LF/HF ratio during CB exposure, suggesting an absence of sympathetic tone. In conclusion, older healthy mice increase cardiac sympathetic tone during PM exposure while terminally senescent mice show a greater PM-induced parasympathetic tone in regulating HR. The significance of the current results suggest that PM-induced HR regulatory changes may ultimately depend on the degree of physiological aging.

Effects of fine particulate on heart rate variability in Beijing: a panel study of healthy elderly subjects

“…Some studies reported positive associations (Riediker et al 2004;Magari et al 2002;Gong et al 2003), whereas others reported the negative Gold et al 2000;Pope et al 2004) or zero association (Sullivan et al 2005;Barclay et al 2009). In our study, PM 2.5 leads to the increase of HRV frequency indices of the healthy elderly subjects in pooled data analysis, which is consistent with some previous epidemiological and animal experimental (Godleski et al 2000;Elder et al 2007;Tankersley et al 2004) (shown in Table 5). Studies on the mechanisms support the positive associations between PM 2.5 exposure and HRV indices.…”

Heart rate variability in rodents: uses and caveats in toxicological studies

“…is used. Some of our recent work in rodents [55,70,71] has utilized the Lomb-type periodogram method due to several specific advantages it possesses. For one, the algorithm generated a good balance of power across the HF range in mice, whereas several other FFT-type algorithms were heavily biased by LF alterations.…”

Comparison of heart rate variability and cardiac arrhythmias in polluted and clean air episodes in healthy individuals

“…Animal studies have also shown different results. Although Chang et al [15] reported an increase in heart rate in rats exposed to concentrated particulate matter, Tankersley [16] and Campen [17] found that air pollutant exposure could be associated with a reduced heart rate in rats compared with the heart rate during clean air exposure. It seems that traffic-related particles can affect autonomic function in healthy subjects, especially those traveling a great deal in the city.…”